1. Field of the Invention
The present invention relates to a control system and associated method for use with prosthetic devices. Particularly, the present invention relates to a prostheses control system and method for below-the-elbow amputees.
2. Description of the Prior Art
Typically, a prostheses aims to give relief to persons disabled by the absence or defect in their body parts. The field of prostheses has most advanced in the area of artificial arms and artificial legs. In particular, artificial arms are required to produce complicated motions. A high degree of perfection has been reached with respect to the use of electric motors and hydraulic drives for operating such artificial arms and legs. The control of a drive mechanism in association with a prosthesis calls for highly complicated processing. Various methods have previously been used and proposed for the purpose of such control.
Much work has been done in the field of prosthetic devices. Prior art devices include the hook and cable system developed in the 1800's and still used today. Hydraulic actuated prostheses and computer controlled "bionic" type devices are available. The disadvantages of prior devices range from only two digit ("hook") control, to lack of wrist control and high frictional forces associated with the cable and hook hardware resulting in extreme complexity, to burdensome maintenance, to questionable reliability, and to exorbitant cost associated with bionic methodology.
Unfortunately, the prior methods and apparatus used in association with the control of prostheses tend to have the common disadvantage that the control devices are unproportionately large in size for the number of modes of motion the artificial limb is expected to produce. Similarly, numerous methods have been proposed for the discrimination of control signals used for causing artificial limbs to produce various motions. Such methods and apparatus have, for example, used a plurality of independent input devices, prescribed voice sounds uttered by the user as instruction signals, bioelectric signals for controlling the motion, feedback circuits for controlling the motion, complicated models, mini-central processing units, varying a cutoff frequency, the use of mechanical structures such as springs and associated stepping motors to simulate finger and wrist motion, and related pressure devices to assist in controlling prostheses.
It is known that most prosthetic limb devices are clumsy, have severe motion limitations, and are unnatural in appearance. Nonetheless, remote manipulators bearing similarities to the forearm and hand have been used in space, planetary exploration, deep-sea work and nuclear research. Most such devices suffer from a high cost, lack of controllability and an inability to reproduce human limb motions. Most remote manipulators of the foregoing types, including the prosthetic devices, are unable to perform typical motions without including significant equipment. Developers have approached the problem along two separate fronts. First, the typical approach is not to use wrist motion at all. Such an approach can be recognized by the use of a claw or hook-type prosthetic. The claw or hook must be rotated about an axis of the arm to align the claw or hook with the object to be grasped. Typically, the prior motion must be followed by orienting the arm such that the object picked up can be held at an acceptable angle relative to vertical. Second, when wrist motion is necessary and the size, weight and cost are not constraints, a gimbaled, azimuth/elevation-type wrist joint has been used.. A two degree of freedom gimbaled wrist manipulator can duplicate the total wrist motion. Even then, with a two degree of freedom gimbaled arrangement, the required placement of drive motors and control devices for this type of manipulator results in a rather large and bulky package.
Artificial limbs are readily attached to a shoulder socket or upper arm. Typically the most favored prosthesis is one which uses the "shrug" control. A shrug-type controller typically includes a hook and cable system which was originally developed in the 1800's. Such systems have only two digit control, lack wrist control and have high frictional forces with respect to the cable and hook hardware. Further, such hardware is complex, difficult to maintain, not reliable and expensive. Nonetheless, the hook and cable, shrug control method is still widely favored by below the elbow amputees. Reasons cited for the widely favored acceptance of shrug control devices include the low cost, the ease of repair, the reliability and the simple pretension of the hook derived from the shoulder/back muscle through a harness and cable assembly.
Typically, such prostheses have a shoulder socket placed on the shoulder stump comprising an elbow joint operated by rods and connected to the shoulder socket, a forearm socket pivotally attached to an elbow joint and provided means for rotating the forearm, and an artificial hand complete with moveable fingers united with the forearm socket. Movements of the arm at the elbow joint and the opening and closing of the fingers are carried out with respect to such prostheses by the aid of the movement of the rods.
Obviously, movement by means of such artificial limbs requires great effort by the wearer of the arm. These efforts are particularly great when opening and closing the fingers of an artificial hand. Further, the possibility of making these movements as restricted as they can be performed only in a number of certain positions of the stump (prostheses). The process of transmitting these efforts from the shoulder and other parts of the body by the aid of rods is very uncomfortable and requires complex and unsightly movements.
Although many prosthetic devices have been developed, one system widely favored by below the elbow amputees is a variation of the "hook and cable system." Reasons for the preferred use of the hook and cable system, cited by experts in this field include low costs, easy repair, reliability, and simple pretension of the hook derived from the shoulder/back muscle through the harness cable assembly.
The advantages of the present invention over the prior devices include: the easy to use "shrug" techniques to generate discrete finger digit control and wrist rotation; the compactness with which the control system can be easily mounted in the body of the prosthetic device; conformal printed circuit type conductors can be employed; improved maintenance; individual finger digit control is proposed instead of hook with cable actuation; wrist rotation capability; hardware programmable; lower cost than conventional prostheses and the use of frictional forces for actuation.
The present invention facilitates easy adaptation by either child or adult users, compensating for the "shrug" distance adjustable by the potentiometer. The "shrug" control envelope may be linear or logarithmic as determined by the integrated circuit selection. The electronic control package of the present invention is quite small in comparison to the prior devices. The electronic control package of the present invention is easily mounted in the prosthetic device and requires no additional containers or carriers to be worn by the user.
Primary to the present invention is the combination of the well known concept of myoelectric control of prosthetic devices to the application of prosthetic arms. This combination results in improved finger and wrist control of the prostheses using a bar graph driver for simple, inexpensive generation of discrete control signals for discriminating and calibrating signals to establish multiple control routines.
It is, therefore, a feature of the present invention to provide a prostheses control system and method which in normal use provides for sequential or specific control of each finger digit, for wrist rotation or the like from signals derived from a transducer actuated by shoulder/back muscle movement.
A feature of the present invention is to provide the user with a "shrug" technique apparatus and method to generate discrete digit and wrist movement.
Another feature of the present invention is to provide a control system that can be easily mounted in the body of the prosthetic device.
Yet another feature of the present invention is to provide novel sensing and electronic control techniques.
Still another feature of the present invention is to provide a high level signal using typical shrug techniques.
Still another feature of the present invention is to provide individual finger digit control with a "shrug" technique as opposed to a "hook" with cable actuation.
Still another feature of the present invention is to provide for individual finger digit control at the same time as wrist rotation capability.
Still another feature of the present invention is to provide hardware programmable prostheses.
Still another feature of the present invention is to provide a low cost prostheses control system.
Still another feature of the present invention is to provide low frictional forces for actuation of the prostheses control system.
Additional features and advantages of the invention will be set forth in part in the description which follows, and in part will become apparent from the description, or may be learned by practice of the invention. The features and advantages of the invention may be realized by means of the combinations and steps particularly pointed out in the appended claims.